1. Field
This invention relates to a method and apparatus for measuring data timing using time-voltage sawtooth ramps.
2. Background
In electronics, as data is being transmitted from a source to a destination, it is important that the destination receive the data accurately. However, depending on various factors such as the type of data, frequency of data, channel between the source and destination, etc., errors or inaccuracies may occur in the received data at the destination.
In digital communications, the “eye diagram” is used to visualize how waveforms used to send multiple bits of data across a channel can potentially lead to errors in the interpretation of those bits at the receiver. This problem of inter-symbol interference is caused by jitter that creates errors in the channel. Jitter is a measure of signal quantity and is defined as the measure of variance in signal characteristics. A zero jitter measurement indicates that the signal transition occurs at exactly the same point in time for each transition.
An eye diagram chops up a received signal into each segment of time and overlays each segment on top of one another. If there is no jitter, the eye diagram looks similar to a stop sign. In contrast, wide super imposed transitions in the eye pattern diagram represents high jitter associated with the signals, implying that the signals are not consistently transitioning at the required time. A small eye width implies a large variance in signal transition time. In designing a channel and for measuring quality of a channel, an eye diagram showing jitter may be used.
Before a channel between a source and a destination is used, it may be simulated to predict the amount of potential jitter. In simulation, successive measurements of voltage at a time are preformed to get the eye diagram mathematically. However, this is problematic in that the waveform must be reconstructed in order to be measured. Moreover, current simulation techniques require a huge amount of measurements. These measurements require the use of a lot of CPU time, simulation time, and disk space. For example, for each simulation/measurement (approximately 1000 runs), data must be analyzed and stored. Each measurement adds to the complexity and time in an exponential manner.
Therefore, a need exists for method and apparatus for detecting eye diagrams and skew on a channel with no requirement to write to disk, and for evaluating the channel in real time.